Polarizer, panel for a liquid crystal display, and liquid crystal display, including a scattering layer

ABSTRACT

Red, green, blue color filters are arranged in sequence in pixel areas of an LCD according to the present invention. Filters, which are scattering particles of a scattering layer, are distributed in a net, and they are distributed in a diagonal direction such that the concentration of the fillers is lower in border areas located between the pixel areas than in the pixel areas.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a polarizer, panel for a liquid crystaldisplay, and liquid crystal display including a scattering layer.

(b) Description of Related Art

A liquid crystal display (LCD) includes a lower panel provided with thinfilm transistors (TFTs), etc., an upper panel provided with colorfilters and a blade matrix, etc., and a liquid crystal layer interposedtherebetween. A plurality of pixel electrodes and a common electrode areformed on the respective panels or on a single panel and supplied withvoltages. The LCD varies the voltages applied to the pixel electrodesand the common electrode to change the orientations of liquid crystalmolecules. In this way, the LCD adjust the transmittance of light anddisplays images.

The liquid crystal material of an LCD has birefringence that therefractive indices in a direction of molecular long axes and in adirection of molecular short axes are different from each other. Due tothe birefringence, the refractive index which the light experiencesdepends on the viewing direction of the LCD, and this differentiates thepolarization of an incident light with linear polarization after passingthrough the liquid crystal. Therefore, the color characteristic and theamount of the light in a slanted direction are different from those in afront direction. In particular, a twisted nematic (TN) LCD sufferssevere problems such as the contrast ratio depending on the viewingangle, color shift, gray inversion, etc., due to the variation of theretardation of the light.

A technique for solving these problems is developed, which compensatesthe phase difference in a specific direction using phase differencecompensation films. This technique is to solve the viewing angle problemby compensating the phase deviation of the light generated by the liquidcrystal in an opposite manner using the compensation films. Then, theviewing angle is ensured in twisted nematic type LCD using the phasedifference compensation films, however, the gray inversion in lowerviewing angle, etc. still remains. To solve this problem, it is proposedto attach a scattering layer to a polarization plate forming the grayinversion. However, broken characters are generated when haze valueindicating the extent of light scattering is high, thereby deterioratingdisplay characteristics.

SUMMARY OF THE INVENTION

A motivation of the present invention is to provide a polarizer, a panelfor an LCD, and a LCD including a scattering layer capable of minimizinggray inversion and eliminating character breaking.

According to the present invention to achieve the motivation, fillers,which are scattering particles inducing light scattering that can beindicated as haze value, forming a scattering layer are distributed in aconcentration having different values in pixel areas and in border areaslocated between the pixel areas.

The scattering layer may be formed on inner or outer surface of a liquidcrystal cell including liquid crystal molecules arranged in twistednematic mode between inner surfaces of two panels.

The LCD may further include upper and lower polarization plates attachedto outer surfaces of the first and the second panels, respectively, andthe upper polarization plate preferably includes an analyzer and firstand second protective films attached on upper and lower sides of theanalyzer, respectively.

The scattering layer may be disposed between the second panel and theupper polarization plate, between the first protective film and theanalyzer, or on the first protective film opposite the analyzer.

The fillers may be distributed in a net, and they are distributedpreferably in a diagonal direction in the pixel areas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an LCD according to an embodimentof the present invention;

FIG. 2 is a layout diagram showing an arrangement of fillers, which arescattering particles of a scattering layer, and red, green, and bluepixels according to an embodiment of the present invention;

FIGS. 3A-3E show steps of a method of manufacturing a polarization plateincluding a scattering layer according to an embodiment of the present;and

FIG. 4 shows a structure of a polarization plate manufactured by amanufacturing method according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein.

In the drawings, the thickness of layers and regions are exaggerated forclarity. Like numerals refer to the elements throughout. It will beunderstood that when an element such as a layer, film, region, substrateor panel is referred to as being “on” another element, it can bedirectly on the other element or intervening elements may also bepresent. In contrast, when an element is referred to as being “directlyon” another element, there are no intervening elements present.

Now, polarizers, panels for an LCD, and LCDs including scattering layersaccording to embodiments of the present invention are described indetail with reference to accompanying drawings.

FIG. 1 is a schematic diagram of an LCD according to an embodiment ofthe present invention.

As shown in FIG. 1, an LCD according to an embodiment of the presentinvention includes lower and upper panels 100 and 200 facing each otherand including pixel areas arranged in a matrix, and a liquid crystallayer 300 interposed therebetween. The dielectric anisotropy Δ∈ of theliquid crystal layer 300 is larger than zero. Liquid crystal moleculesin the liquid crystal layer 300 have a twisted nematic configurationthat the long axes of the liquid crystal molecules are parallel to thesurfaces of the panels 100 and 200 and spirally twisted from one panelto the other in absence of electric field, and the liquid crystalmolecules are oriented under application of electric field with asufficient strength to the liquid crystal layer 300 such that long axesof the liquid crystal molecules are perpendicular to the surfaces of thepanels 100 and 200 and parallel to the electric field.

The lower panel 100 includes a plurality of pixel electrodes forperforming display operation formed on pixel areas arranged in a matrixand made of transparent conductive material and reflective conductivematerial, a plurality of gate lines and a plurality of data linesintersecting each other to define the pixel areas and transferringscanning signals and image signals, respectively, a plurality of TFTselectrically connected to the gate lines and the data lines andcontrolling the image signals from the data lines in response to thescanning signals from the gate lines, etc. The lower panel 100 is calledTFT array panel A lower polarization plate 420 is attached to an outersurface of the lower panel 100.

The upper panel 200 includes a black matrix blocking the light leakagebetween the pixel areas and having openings corresponding to the pixelareas, a plurality of red, green, and blue color filters sequentiallyarranged in the pixel regions, and a common electrode supplied with apredetermined voltage for driving the liquid molecules in cooperationwith the pixel electrodes and made of transparent conductive materialsuch as ITO (indium tin oxide) or IZO (indium zinc oxide). An upperpolarization plate 410 polarizing the light passing therethrough isattached to an outer surface of the upper panel 200 of the two panels100 and 200.

Here, transmission axes of the polarization plates 410 and 420 attachedto the outer surfaces of the two panels 100 and 200 may be parallel toor perpendicular to each other.

Compensation films 510 and 520 are attached between the lower and theupper polarization plates 410 and 420 and a liquid crystal cell 100, 200and 300, respectively, and the compensation films 510 and 520 compensatethe phase change of the light in the liquid crystal layer 300, therebysecuring wide viewing angle.

The lower polarization plate 420 includes a polarizer or an analyzercontaining PVA (poly vinyl alcohol) and iodine, and protective films(TAC: Tri acetate cellulose) attached to upper and lower surfaces of thepolarizer, respectively. Moreover, the upper polarization plate 410includes an analyzer 412 containing PVA and iodine and protective films411 and 413 attached to upper and lower surfaces of the analyzer 412. Inaddition, a scattering layer 414 including scattering particles calledfillers are formed on the upper protective film 413 of the upperpolarization plate 410.

The scattering layer 414 may be formed on or under the lower protectivefilm 411, between the upper panel 200 and the upper compensation film510, or between the upper protective film and the analyzer 412.

Here, the scattering layer 414 scatters the light passing through theliquid crystal cell 100, 200, and 300 to all directions to equalize thelight. Preferably, the haze value of the scattering layer 414 is equalto or more than 50. It is because that gray inversion in the lowerdirection can be effectively improved if the haze value of thescattering layer 414 is equal to or more than 50.

However, display characteristic may be deteriorated by generation ofcharacter breaking in case that the haze value of the scattering layer414 is equal to or more than 50. According to the embodiment of thepresent invention to solve such problem, fillers, which are scatteringparticles of the scattering layer 414, are distributed in differentconcentration in pixel areas and border areas between adjacent pixelareas. In detail, the concentration in the border areas between thepixel areas is lower than that in pixel areas. Then, the lightscattering in the border areas between pixel areas is minimized suchthat the gray inversion is minimized by adopting a haze value equal toor higher than fifty and the character breaking is eliminated. Now, thisconfiguration is described in detail with reference to the figures.

FIG. 2 is a layout diagram showing an arrangement of the fillers, whichare scattering particles of the scattering layer, and red, green, andblue pixels according to an embodiment of the present invention.

As shown in FIG. 2, a plurality of red, green and blue color filters R,G, and B are arranged in sequence in pixel areas of a liquid crystalcell 100, 200, and 300 (shown in FIG. 1) according to an embodiment ofthe present invention. Here, scattering particles of the scatteringlayer 414, i.e., fillers 4123 are distributed in a net with a highconcentration, and the intersections of the diagonals are preferablyplaced on border areas between the pixel areas such that the borderareas between the pixel areas have a lower concentration of the fillers423 than that in pixel areas. Although the fillers are distributed in anet with a high concentration, the fillers can have various arrangement.

In an LCD according to an embodiment of the present invention, a lightlinearly polarized by the lower polarization plate 420 attached on thelower panel 100 varies its polarization when passing through the liquidcrystal layer 300. The light is linearly polarized again by the upperpolarization plate 410 attached on the upper panel 200, and it isscattered to all directions by the scattering layer 414. Therefore, theamount and the color characteristics of the light do not depend on theviewing angle and thus negative phenomena such as color shift, grayinversion, etc. are minimized. Moreover, since the concentration of thefillers 423 in the border areas between the pixel areas is lower thanthe concentration of the fillers 423 distributed in the pixel areas, thelight scattering in the border areas between the pixel areas can beminimized to eliminate the character breaking.

The scattering layer 414 is formed by attaching a scattering film to theouter surface of the polarization plate 410 facing the liquid crystalcell 10 and 20 as in the present invention, by applying light diffusionadhesive having light scattering function when the polarization plate410 is attached to the upper panel 200, or by forming a light scatteringlayer made of resin containing minute dispersed particles on the colorfilters, and it may be formed with surface treatment of the upperprotective film 413 of the upper polarization plate 410. Now, this willbe described in detail with reference to the drawings.

FIGS. 3A-3E sequentially show steps of a manufacturing method of apolarization plate including a scattering layer according to anembodiment of the present, and FIG. 4 shows a structure of apolarization plate manufactured by the manufacturing method according toan embodiment of the present invention.

FIG. 3A shows the step of forming a scattering layer 414 on an upperprotective film 413 (shown in FIGS. 1 and 2) among the steps of amanufacturing method of a polarization plate including a scatteringlayer according to an embodiment of the present invention. The upperprotective film 413 moves in a direction indicated by an arrow using afirst support 600 and a second support 700. A third roller 500 coatedwith scattering material including fillers and binder or acrylic rotatesand contacts the upper protective film 413 to form a scattering layer414 on the upper protective film 413, and the scattering layer 414 ishardened by UV (ultra violet) ray.

In order to obtain high concentration of the fillers 423 in a net in thescattering layer 414 as shown in FIG. 2, first, the concentration of thefillers 423 in a horizontal direction becomes high through a step Ashown in FIG. 3B, and then the concentration of the fillers 423 in avertical direction becomes high through a step B shown in FIG. 3C. Then,the upper protective film 413 including the scattering layer 414containing the fillers 423 densely distributed in the horizontal and thevertical directions is obtained as shown in FIG. 3D.

The scattering layer 414 having fillers and binder or acrylic is coatedto have protrusions in a net such that the concentration of the fillers423, the scattering particles, is high along lines. Then, fillerparticles are gathered densely in the binder or acrylic protrusions,while they are distributed sparsely or scarcely in other parts. Thefillers 423, the scattering particles have high refractive index, whilethe binder has low refractive index. Then, the protrusions function asconcave lenses, and incident light is radially scattered by the fillers.

The upper protective film 413 is then cut to be attached onto the liquidcrystal cell 100, 200 and 300, as shown in FIG. 3E, along lines making45 degrees with edges of the upper protective film 413. Finally, theupper protective film 413 having a light scattering layer 414 containingthe fillers 423 (shown in FIG. 2) distributed in diagonal directions inpixel areas as shown in FIG. 4 is manufactured.

As described above, the present invention makes the concentration ofscattering particles, which are contained in a light scattering layerfor inducing scattering to minimize gray inversion, be lower in borderareas between pixel areas, thereby eliminating the gray inversion andpreventing character breaking to improve display characteristic of adisplay device.

1. A panel for liquid crystal display comprising: a plurality of pixelareas arranged in a matrix; and a scattering layer defining an outersurface of the panel, the scattering layer containing fillers forinducing light scattering indicated as haze value, wherein the fillersare distributed in a concentration having different values in the pixelareas and in border areas located between the pixel areas.
 2. The panelof claim 1, wherein the concentration of the fillers in the border areasis lower than that in the pixel areas.
 3. A polarization plate forliquid crystal display, the polarization plate comprising: an upperprotective film including fillers that are formed inside the upperprotective film or are formed on at least one surface of the upperprotective film for inducing light scattering indicated as haze value,the fillers distributed in a concentration different between in pixelareas and in border areas located between the pixel areas; an analyzerhaving a first surface, on which the upper protective film is attached,and a second surface facing the first surface; and a lower protectivefilm attached to the second surface of the analyzer.
 4. The polarizingplate of claim 3, wherein the concentration of the fillers is lower inthe border areas than in the pixel areas.
 5. A liquid crystal displaycomprising: a first and a second panels facing each other and havingpixel areas arranged in a matrix; a liquid crystal layer interposedbetween the first panel and the second panel; and a scattering layerformed on an outer surface of the second panels and containing fillersfor inducing light scattering as haze value, the fillers in aconcentration different between in the pixel areas and in border areaslocated between the pixel areas.
 6. The liquid crystal display of claim5, wherein the concentration of the fillers is lower in the border areasthan in the pixel areas.
 7. The liquid crystal display of claim 6,further comprising upper and lower polarization plates attached to outersurfaces of the first and the second panels, respectively.
 8. The liquidcrystal display of claim 7, wherein the upper polarization platecomprises an analyzer and first and second protective films attached onupper and lower surfaces of the analyzer, respectively.
 9. The liquidcrystal display of claim 8, wherein the scattering layer is disposedbetween the second panel and the first protective film or on the firstprotective film opposite the analyzer.
 10. The liquid crystal display ofclaim 5, wherein the fillers of the scattering layer are distributed ina net.
 11. The liquid crystal display of claim 10, wherein the fillersare distributed in a diagonal direction in the pixel areas.
 12. Thepanel of claim 11, wherein the parts of intersection of the fillers arelocated on a long side of the border area.
 13. The panel of claim 1,wherein the fillers of the scattering layer are distributed in a net.14. The panel of claim 13, wherein the fillers are distributed in adiagonal direction in the pixel areas.
 15. The panel of claim 14,wherein the parts of intersection of the fillers are located on a longside of the border area.